transcode_for_browser: overwrite in-place to suppress Gradio fallback converter

app.py

@@ -159,7 +159,8 @@ def strip_audio_from_video(video_path: str, output_path: str) -> None:
 def _transcode_for_browser(video_path: str) -> str:
     """Re-encode uploaded video to H.264/AAC MP4 so the browser preview widget can play it.
 
-    Returns the transcoded path on success, or the original path if transcoding fails.
+    Overwrites the original file in-place so Gradio serves the H.264 version
+    and does NOT trigger its own slow fallback conversion.
     Only called on upload — not during generation.
     """
     if video_path is None:
@@ -167,7 +168,14 @@ def _transcode_for_browser(video_path: str) -> str:
     try:
         probe     = ffmpeg.probe(video_path)
         has_audio = any(s["codec_type"] == "audio" for s in probe.get("streams", []))
-        out_path  = video_path.rsplit(".", 1)[0] + "_preview.mp4"
+        # Check if already H.264 — skip transcode if so
+        video_streams = [s for s in probe.get("streams", []) if s["codec_type"] == "video"]
+        if video_streams and video_streams[0].get("codec_name") == "h264":
+            print(f"[transcode_for_browser] already H.264, skipping")
+            return video_path
+        # Write to a temp file first, then replace original in-place.
+        # This avoids Gradio's own fallback converter triggering on the H.265 source.
+        tmp_path  = video_path + ".tmp.mp4"
         kwargs = dict(
             vcodec="libx264", preset="fast", crf=18,
             pix_fmt="yuv420p", movflags="+faststart",
@@ -178,10 +186,13 @@ def _transcode_for_browser(video_path: str) -> str:
         else:
             kwargs["an"] = None
         # map 0:v:0 explicitly to skip non-video streams (e.g. data/timecode tracks)
-        ffmpeg.input(video_path).output(out_path, map="0:v:0", **kwargs).run(
+        ffmpeg.input(video_path).output(tmp_path, map="0:v:0", **kwargs).run(
             overwrite_output=True, quiet=True
         )
-        return out_path
+        import os as _os
+        _os.replace(tmp_path, video_path)
+        print(f"[transcode_for_browser] transcoded to H.264 in-place: {video_path}")
+        return video_path
     except Exception as e:
         print(f"[transcode_for_browser] failed, using original: {e}")
         return video_path